Melting ice puts emperor penguins on a slippery slope

This will not be the emperor penguins’ favourite century

(Image: Frans Lanting/FLPA)

Antarctica’s iconic emperor penguins are predicted to go into decline this century. Rising temperatures will melt the sea ice on which they live and breed, and as a result two-thirds of the colonies could halve in size by 2100. The question now is whether the penguins can survive by moving to new breeding grounds.

So far only one colony, at Adélie Land in east Antarctica, has been studied in detail. It is expected to decline as the climate warms. The others have been spotted from space – thanks to the huge black guano stains the penguins leave on the ice – but have never been visited by humans.

Hal Caswell of the Woods Hole Oceanographic Institution in Massachusetts and his colleagues used data from Adélie Land to extrapolate what would happen to all emperors. They projected how global warming this century will affect the sea ice near each colony.

The sea ice is key to the penguins’ survival, says Caswell. Too much ice forces them to travel great distances to find food for their young, but too little means there is less food, as the krill they eat also rely on sea ice.

Where’s my ice?

Most colonies will grow until around 2040, but then the accelerating retreat of the sea ice will cause them all to decline. Overall, it looks like the total population will fall 19 per cent by 2100. And two-thirds of the colonies are projected to halve in population – for instance those at Queen Maud Land and Enderby Land facing the Indian Ocean – because they will lose more sea ice than others.

“If emperor penguin colonies were bank accounts, they would all be showing negative returns by the end of the century,” says Caswell.

Other researchers agree that global warming will be bad news for the emperors. But the decline may be slower than Caswell’s model suggests, because penguins are adaptable.

Caswell’s model assumes that individual penguins always return to the same breeding grounds, so they will perish if their site deteriorates. “[Their] model assumes each colony is a closed population, with no immigration or emigration elsewhere,” says David Ainley of Penguin Science, an educational programme based in the US.

Moving home

But if the penguins can move to new breeding grounds, they may have a better chance. And according to Michelle LaRue at the University of Minnesota at St Paul, they can.

“It appears that the emperors have the ability to move among colonies,” says LaRue. That means some colonies, assumed to have been wiped out, may have simply relocated. LaRue presented her results at the Ideacity conference in Toronto, Canada, last week. They will be published soon in Ecography.